??W2 Econo valves??

How can that be? Wouldn't two different length valves require different rocker arms? If I run standard length valves, I assume I can run the standard offset rockers for the Econo head. But, if I use the long valves and taller springs, can I still use the same rockers? I guess I would run the standard length valves due to them being more commonly produced if they both work on my heads. I've seen other posts here saying things like "It depends on what size the rocker hold down bolt is". I just don't want to end up buying the wrong length valves.